This invention relates generally to xerographic copying apparatus and, more particularly, to a contact fusing system for fixing electroscopic toner material to a support member.
In the process of xerography, a light image of an original to be copied is typically recorded in the form of a latent electrostatic image upon a photosensitive member with subsequent rendering of the latent image visible by the application of electroscopic marking particles, commonly referred to as toner. The visual image can be either fixed directly upon the photosensitive member or transferred from the member to a sheet of plain paper with subsequent affixing of the image thereto.
In order to permanently affix or fuse electroscopic toner material onto a support member by heat, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This action causes the toner to be absorbed to some extent into the fibers of the support member which, in many instances, constitutes plain paper and in other instances constitutes cellulose acetate or polyester film. Thereafter, as the toner material cools, solidification of the toner material occurs causing the toner material to be firmly bonded to the support member. In both the xerographic as well as the electrographic recording arts, the use of thermal energy for fixing toner images onto a support member is old and well known.
One approach to thermal fusing of electroscopic toner images onto a support has been to pass the support with toner images thereon between a pair of opposed roller members, at least one of which is internally heated. During operation of a fusing system of this type, the support member to which the toner images are electrostatically adhered is moved through the nip formed between the rolls with the toner image contacting the fuser roll to thereby effect heating of the toner images within the nip.
Heretofore, the surface of the fuser roll structure of contact fuser assemblies have been fabricated from one of various materials, for example, Teflon, silicone rubber, and certain metals such as copper. Experience with such materials has shown that certain difficulties arise when a particular substrate is employed with a particular surface material. For example, when transparencies which utilize polyester film-type material have toner images fused thereto by a metal surface roll the transparency exhibits halos around thick lined images because the substrate is not flexible enough to conform to the sudden change in toner pile height. Moreover, it is difficult to strip high pile, continuous tone images from the hard fuser roll as the plasticized toner flows into the fuser roll surface. This confirmation of the toner image to the fuser roll not only results in stripping difficulties but also imparts a finish to the toner surface which corresponds to the surface of the fuser roll. Thus, if the roll is smooth a high gloss image is obtained.
On the other hand, when a fuser roll surface comprises an elastic material such as silicone rubber or Viton the fused image exhibits a matte finish on plain paper which does not appeal to most people utilizing xerographic apparatus.
Accordingly, the primary object of this invention is to provide a new and improved apparatus for fusing toner images.
It is a more particular object of this invention to provide a new and improved fuser apparatus for fixing toner images to various substrates.
Another object of this invention is to provide a fuser apparatus comprising a plurality of fuser roll structures forming a pair of nips through which substrates are moved in order to fuse the images and wherein the substrates of one type are passed through one of the nips while substrates of another type are passed through the other of the nips whereby the substrate and toner images carried thereby contact different surfaces depending upon the substrate.